Field of the Invention
The present invention relates to an object information acquiring apparatus.
Description of the Related Art
Photoacoustic tomography (PAT) is one of the methods for obtaining an optical characteristic value (e.g., an absorption coefficient) of the inside of an object such as a living body. When pulsed light that is generated from a light source is radiated to a living body, the light propagates while diffusing through the inside of the living body. A light absorber within the living body absorbs the propagating light and generates a photoacoustic wave. The photoacoustic wave is received by a probe, and this received signal is analyzed, to acquire an initial sound pressure distribution originated from the light absorber of the living body. An absorption coefficient distribution can be obtained from the initial sound pressure distribution by using the following formula (1), where P0 represents the initial sound pressure, Γ the Gruneisen coefficient, μa the absorption coefficient, and ϕ the fluence of light.μa(r)=P0(r)/{Γ·ϕ(r)}  (1)
As is clear from this formula (1), the fluence of light needs to be figured out correctly in order to accurately obtain the absorption coefficient distribution. Unfortunately, it is not easy to directly measure the fluence of light radiated to the object while the object is being measured. Therefore, the fluence of light radiated to the object is measured indirectly based on the outputs of the light source and the transmissivity of the optical components between the light source and the object.
However, since the measurement accuracy of this method drops as the optical components deteriorate, a decline of the transmission efficiency triggered by the deterioration of the optical components needs to be figured out. According to the technique disclosed in Japanese Patent Application Laid-Open No. H10(1998)-193146, part of the fluence of light entering an optical fiber and part of the fluence of light emitted from the optical fiber are measured at all times, and when the ratio therebetween falls below a predetermined value, it is determined that the optical fiber has deteriorated. Such determination is to encourage replacement of the optical fiber so that the transmission efficiency can be kept within a certain range.
Patent Literature 1: Japanese Patent Application Laid-Open No. H10(1998)-193146